The present disclosure relates to a mobile lifting crane that uses a rigging winch drum and rigging to help assemble a folded jib main strut when a luffing jib is employed on the crane. Furthermore, the disclosure relates to the disassembly and assembly of the luffing jib struts on a job site in a way that allows the sheaves of strut caps to remain reeved during transport to or from the job site, to prevent re-reeving the strut caps at a new job site.
Mobile lift cranes typically include a carbody having moveable ground engaging members; a rotating bed rotatably connected to the carbody such that the rotating bed can swing with respect to the ground engaging members; a boom pivotally mounted on a front portion of the rotating bed, with a load hoist line extending therefrom, and counterweight to help balance the crane when the crane lifts a load. Additionally, when the crane needs to work on particularly high buildings or structures, or in restricted spaces, a luffing jib pivotally mounted at the top of the boom may be extended out to provide required reach. When the luffing jib is employed, one or more luffing jib struts are connected to the top of the boom or bottom of the luffing jib. These struts support the luffing jib rigging and backstay straps, providing a moment arm about which force can be applied to raise the jib and support a load being lifted by the luffing jib.
Since the crane will be used in various locations, it needs to be designed so that it can be transported from one job site to the next. This usually requires that the crane be dismantled into components that are of a size and weight that they can be transported by truck within highway transportation limits. The ease with which the crane can be dismantled and set up has an impact on the total cost of using the crane. Thus, to the extent that fewer man-hours are needed to set up the crane, there is a direct advantage to the crane owner or renter. When the luffing jib rigging includes multiple parts of line between the struts, each strut cap usually includes multiple sheaves through which the jib hoist line must be reeved whenever the crane is set up, which takes a significant amount of time.
Several methods have been used in the past to assemble the luffing jib with its luffing jib struts. At least one of those methods involves attaching the assembled jib struts to the end of the boom and reeving the caps of the jib struts with a jib hoist line. The reeving process is time consuming. A whip hoist line may then be used to pull the top of the two jib struts (the jib main strut) over center while it is raised with an assist crane to the point that a backstay suspension, connected at the base of the boom, can be pinned to the top of the main strut. The assist crane must travel while it lifts to perform this lifting operation, and assemblers need to work high off the ground in pinning the backstay suspension, which may lengthen the process and puts the assemblers at more risk.
Accordingly, the present disclosure includes solutions to the above drawbacks with previous methods by making the method for assembly of the jib struts more efficient and safer. For instance, the need to re-reeve the jib strut caps during set up of the crane on the job site is eliminated, the assist crane need not travel when erecting the main strut, and the assembly steps may be executed closer to the ground.